Electrical discharge machining is generally also known by the acronym EDM. Its miniaturization (micro-EDM or μEDM) has different variants depending on the shape of the etching electrode (which here below will also be called here a micro-electrode). These variants are the following:                Die-sinking micro-electrical discharge machining in which a microelectrode with a shape complementary to the shape to be machined is sunken into the part.        Wire micro-electrical discharge machining with a conductive wire circulating or driven by an alternating motion.        The drilling of holes by micro-electrical discharge machining with a tip electrode or a tube electrode.        Milling micro-electrical discharge machining better known as milling EDM.        
Milling micro-electrical discharge machining does not necessarily imply a rotational motion of the microelectrode or machined part.
Here below in this description, whenever “micro-electrical discharge machining” is mentioned, reference is being made to a technology corresponding to milling micro-electrical discharge machining.
The present filing party knows machines for machining a part by micro-electrical discharge machining having a machining configuration in which a tip of an etching electrode is plunged into a bath of (insulating) dielectric fluid bathing one face to be machined of the part in order to carry out a machining of this part by micro-electrical discharge machining. This tip is small enough to enable the etching of grooves in the face whose cross-width is greater than 10 μm.
For machining complex shapes, the electrode describes a three-dimensional path in gradually removing material from the part, as would be done by a micro-mill in a chip-removal method. The difference is that the elementary action of removing material is not a mechanical action but a thermal action produced by an electrical arc. The cutting action is swift. The cooling is obtained by the dielectric fluid bath filling the space crossed by the electrical arc between the etching electrode and the part to be machined. This space is called a “gap”.
Micro-electrical discharge machining can be used to machine all conductive materials (steel, titanium etc) and semi-conductive materials (silicone, silicone carbide etc). It enables especially the machining of hard metals which cannot be machined by classic methods. Indeed, there is no mechanical contact between the electrode and the part to be machined.
Micro-electrical discharge machining can be distinguished from prior-art electrochemical corrosion methods known as electrochemical machining (ECM) by the need to create a major difference in potential between the etching electrode and the part to be machined. To create this difference in potential, the dielectric fluid has to fill the gap. Conversely, electrochemical machining is based on an oxidation reaction prompted by a current flowing between the etching electrode and the part to be machined. In order that the current may be set up, the etching electrode and the part to be machined are plunged into an electrolyte bath, i.e. a bath of a conductive fluid. The electrochemical corrosion can be produced by a current which flows between the etching electrode and the part to be machined or by discharges of current between these two elements. During the machining of a part by electrochemical corrosion, the wearing out of the electrode is often negligible. This is not the case in the electrical discharge machining method where it can happen that the wearing out of the electrode is not negligible.
In the case of milling by micro-electrical discharge machining, the electrode follows a machining path to machine the face of a part. The great value of this method is that the machining path may have several variations in height relatively to the face of the part to be machined or may even vary continuously. When this machining path has several variations in height relatively to the face of the part to be machined, it is said here that the machining is three-dimensional machining. Three-dimensional machining is done by making imprints, holes or non-through grooves the depths of which relatively to the face of the part vary in stages. This can be obtained directly from a digital definition obtained by computer-assisted design, thus preventing the manufacture of complex and costly toolings (which is the case for example with die sinking micro-electrical discharge machining). In general, high shape factors (ratio of the drilling depth to the drilling diameter) can be obtained by this method, giving typically shape factors of more than 10 or 100.
As shall be seen here below, the manufacture of electrodes limits the development of this method while potential applications are very great. Indeed, by principle, micro-electrical discharge milling makes it possible to envisage for example:
the machining of toolings:                hard-steel molds for microplasturgy        master models for microstamping        metal imprints by hot embossing or micro-hot-embossing.        
machining of micro-parts:                micro-turbines made out of very hard materials,        micro-heat-exchangers,        medical parts made of titanium (for example microstents)        diesel injection nozzles etc.        
Specifically, in the field of micro-nanotechnologies, milling micro-electrical machining is used to machine materials little used in this field (titanium, SiC, diamond etc) with very high resolution, and at low cost. Furthermore, it is very difficult by classic techniques of microtechnology (FIB, RIE etc) to machine semi-conductive materials with a high shape factor, the main technique used in this case being designated by the acronym LIGA (Lithografie Galvanoformung Abformung or Lithography Electroplating and Molding) which is very costly. It is even impossible with these techniques to carry out machining with a continuous variation in depth (the number of photolithography masks is always limited in microtechnology). Thus, even silicon machining could derive benefit from milling micro-electrical discharge machining provided that it is easy to use electrodes with sufficiently fine tips, i.e. with diameters of less than 10 μm.
Now, in the prior art, electrodes for milling by micro-electrical discharge machining are wires, tips or tubes with a diameter of over 20-40 μm. Indeed, these microelectrodes are made finer by mechanical machining (polishing for example) by reverse electrical discharge machining or again by wire micro-electrical discharge machining with a circulating wire electrode. Specifically, in the case of the piercing of holes by micro-electrical discharge machining, demonstrations of principle have been made with 5 μm electrodes but this principle has not been extended to the machining of complex shapes. Finally, in the case of wire micro-electrical discharge machining, the diameter of the wire is limited in practice to 20 μm because of problems of mechanical strength.
The etching electrodes used for carrying out micro-electrical discharge machining are very small. These electrodes get worn out during micro-electrical discharge machining. They therefore need to be frequently replaced. This replacement of electrodes is a complicated task because of the small size and brittleness of these electrodes. For example, this replacing of electrodes is done by hand after each machining operation. These difficult operations for replacing electrodes therefore limit the productivity of current machining toolings using micro-electrical discharge machining.
The present invention generally seeks to mitigate the defects of the prior art by proposing a machining tool with a resolution of less than 10 μm and increased productivity.